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<title>t_rcvudata</title>
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The Single UNIX &reg; Specification, Version 2<br>
Copyright &copy; 1997 The Open Group

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<h4>NAME</h4><blockquote>
t_rcvudata - receive a data unit
</blockquote><h4>SYNOPSIS</h4><blockquote>
<pre><code>

#include &lt;<a href="xti.h.html">xti.h</a>&gt;

int t_rcvudata(
    int fd,
    struct t_unitdata *unitdata,
    int *flags)
</code>
</pre>
</blockquote><h4>DESCRIPTION</h4><blockquote>
<pre>
<P><table  bordercolor=#000000 border=1 align=center><tr valign=top><th align=center><b>Parameters</b>
<th align=center><b>Before call</b>
<th align=center><b>After call</b>
<tr valign=top><td align=left>fd
<td align=center>x
<td align=center>/
<tr valign=top><td align=left>unitdata-&gt
<td align=center>addr.maxlen
<td align=center>x
<tr valign=top><td align=left>unitdata-&gt
<td align=center>addr.len
<td align=center>/
<tr valign=top><td align=left>unitdata-&gt
<td align=center>addr.buf
<td align=center>?
<tr valign=top><td align=left>unitdata-&gt
<td align=center>opt.maxlen
<td align=center>x
<tr valign=top><td align=left>unitdata-&gt
<td align=center>opt.len
<td align=center>/
<tr valign=top><td align=left>unitdata-&gt
<td align=center>opt.buf
<td align=center>?
<tr valign=top><td align=left>unitdata-&gt
<td align=center>udata.maxlen
<td align=center>x
<tr valign=top><td align=left>unitdata-&gt
<td align=center>udata.len
<td align=center>/
<tr valign=top><td align=left>unitdata-&gt
<td align=center>udata.buf
<td align=center>?
<tr valign=top><td align=left>flags
<td align=center>/
<td align=center>x
</table>
</pre>
<p>
This function is used in connectionless-mode
to receive a data unit from another transport
user.
The argument
<I>fd</I>
identifies the local transport endpoint through which data will be
received,
<I>unitdata</I>
holds information associated with the received data unit, and
<I>flags</I>
is set on return to indicate that the complete data unit was not
received.
The argument
<I>unitdata</I>
points to a
<B>t_unitdata</B>
structure containing the following members:
<pre>
<code>
struct netbuf addr;
struct netbuf opt;
struct netbuf udata;
</code>
</pre>
<p>
The
<I>maxlen</I>
field of
<I>addr</I>,
<I>opt</I>
and
<I>udata</I>
must be set before calling this function to indicate the maximum
size of the buffer for each.
If the 
<I>maxlen</I>
field of 
<I>addr</I>
or 
<I>opt</I>
is set to zero, no information is returned in the 
<I>buf</I>
field of this parameter.
<p>
On return from this call,
<I>addr</I>
specifies the protocol address of the sending user,
<I>opt</I>
identifies options that were
associated with this data unit, and
<I>udata</I>
specifies the user data that was received.
<p>
By default,
<i>t_rcvudata()</i>
operates in synchronous mode and will
wait for a data unit to arrive if none is currently available.
However, if O_NONBLOCK is set (via
<i><a href="t_open.html">t_open()</a></i>
or
<i><a href="fcntl.html">fcntl()</a></i>),
<i>t_rcvudata()</i>
will execute in asynchronous mode and will fail
if no data units are available.
<p>
If the buffer defined in the
<I>udata</I>
field of
<I>unitdata</I>
is not large enough to hold the current data unit,
the buffer will be filled and T_MORE will be set in
<I>flags</I>
on return to indicate that another
<i>t_rcvudata()</i>
should be called to retrieve the rest of the data unit.  Subsequent calls to
<i>t_rcvudata()</i>
will return zero for the length of the address and options
until the full data unit has been received.
<p>
If the call is interrupted,
<i>t_rcvudata()</i>
will return [EINTR] and no datagrams will have been removed from the endpoint.
</blockquote><h4>VALID STATES</h4><blockquote>
T_IDLE
<br>
</blockquote><h4>ERRORS</h4><blockquote>
On failure,
<I>t_errno</I>
is set to one of the following:
<dl compact>

<dt>[TBADF]<dd>The specified file descriptor does not refer to a transport endpoint.

<dt>[TBUFOVFLW]<dd>The number of bytes allocated for the incoming protocol address or
options
<I>(maxlen)</I>
is greater than 0 but not
sufficient to store the information.
The unit data information to be returned in
<I>unitdata</I>
will be discarded.

<dt>[TLOOK]<dd>An asynchronous event has occurred on this transport endpoint and requires
immediate attention.

<dt>[TNODATA]<dd>O_NONBLOCK
was set, but
no data units are currently available from the transport provider.

<dt>[TNOTSUPPORT]<dd>This function is not supported by the underlying transport
provider.

<dt>[TOUTSTATE]<dd>The communications endpoint referenced by 
<I>fd</I>
is not in one of the states in which a call to this function is valid.

<dt>[TPROTO]<dd>This error indicates that a communication problem has been detected between
XTI and the transport provider for which there is no other suitable XTI
error
<I>(t_errno)</I>.

<dt>[TSYSERR]<dd>A system error has occurred during execution of this function.

</dl>
</blockquote><h4>RETURN VALUE</h4><blockquote>
Upon successful completion, a value of 0 is returned.  Otherwise,
a value of -1 is returned and
<I>t_errno</I>
is set to indicate an error.
</blockquote><h4>SEE ALSO</h4><blockquote>
<i><a href="fcntl.html">fcntl()</a></i>,
<i><a href="t_alloc.html">t_alloc()</a></i>,
<i><a href="t_open.html">t_open()</a></i>,
<i><a href="t_rcvuderr.html">t_rcvuderr()</a></i>,
<i><a href="t_sndudata.html">t_sndudata()</a></i>.
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UNIX &reg; is a registered Trademark of The Open Group.<br>
Copyright &copy; 1997 The Open Group
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